Scientific Realism: Some
Arguments

Philosophy of Science

The first three arguments are all more or less present in, or at least
suggested by, Maxwell's essay. The fourth is also discussed by van Fraassen, but
doesn't seem to be explicitly discussed by Maxwell.

1. Argument from Continuity

1. We should believe in observable entities
2. There is no sharp dividing line between observable and unobservable
So, 3. We should believe in "unobservable" entities also.

Van Fraassen's reply: this is a slippery slope argument (or, to use a
fancier term, a sorites argument). It's no better than Sextus's argument
that incest is OK, or the argument that everyone is bald.

2. Argument from Observability in Principle

1. We should believe in the existence of the observable entities that our
theories invoke
2. "observable" means "can be observed"
3. Everything can be observed (if our technology or our sense organs improve
enough)
So, 4. We should believe in the existence of every entity our theories
invoke

van Fraassen's reply: van Fraassen would reject either 2 or 3, depending
on how we understand "can be observed." 2 is correct if "can be observed"
means "can be detected by contemporary humans with unaided sense organs."
But in that case 3 is incorrect. 3 would be correct if "can be observed"
meant something like "can be detected by humans with the aid of present or
future technology," but then 2 would be incorrect.

Also, according to van Fraassen, advances in technology will not make
more things observable.
On his view, we don't observe things through a microscope, for instance. The
only change that would make something previously unobservable become
observable would be a change in our sense organs, or else bringing into our
epistemic community other beings with better sense organs than ours.

3. Argument from Epistemic Unimportance

1. We should believe in the existence of the observable entities that our
theories invoke
2. The observable/unobservable distinction has no epistemic importance
So, 3. We should believe in the existence of all the entities invoked by our
theories

van Fraassen obviously rejects premise 2. Is there a way to argue about 2
in a more persuasive way than "yes it is" vs. "no it isn't"?

4. Argument from Inference to the Best Explanation

1. We should believe the theory that best explains the evidence
("inference to the best explanation" or "abduction")
2. The theory that best explains the evidence invokes unobservable entities
So, 3. We should believe in the existence of unobservable entities

van Fraassen rejects premise 1. He argues that we should accept the
theory that best explains, but acceptance doesn't require belief in all of
the theory, just in the claims the theory makes about observables.

This is related to van Fraassen's rejection of the idea that explanatory
power is an empirical virtue: he classes it instead as a pragmatic virtue.
What makes him a (constructive) empiricist is the idea that only empirical
virtues give reasons for belief.

Pragmatic virtues may give practical
reasons for accepting one theory over another, but that doesn't give us a
reason to think that the claims about unobservables of the theory are
literally true.